Seek trajectory generation using adaptive filtering

ABSTRACT

Embodiments of the present invention provide a method and a system for generating optimal feedforward signal for the seek control to suppress the RTV (Random Transient Vibrations) and the seek acoustic noise. One aspect is directed to a method of providing a revised feedforward signal using an adaptive filter in a feedforward control system for controlling an actuator to move a head to seek a track and settle on the track of a disk in a disk drive apparatus. The method comprises performing a seek operation of the head using an initial feedforward signal; obtaining an error signal at settling after performing the seek operation; determining filter characteristics of the adaptive filter to minimize the error signal; and implementing the adaptive filter having the determined filter characteristics in the feedforward control system to produce a revised feedforward signal for controlling the actuator for moving the head in the disk drive apparatus.

CROSS-REFERENCES TO RELATED APPLICATIONS

NOT APPLICABLE

BACKGROUND OF THE INVENTION

This invention relates generally to hard disk drive control and, moreparticularly, to seek trajectory generation using adaptive filtering.

Computer hard disk drives (HDDs) include one or more disks of magneticstorage medium and a disk drive head assembly to read and write data onthe magnetic storage medium. Read/write heads typically include a writeelement comprised of a thin film inductive head and a read elementcomprised of a Magnetoresistive (MR) sensor. The heads for the disksurfaces of the disk drive are affixed to an actuator or arm that glidesacross the disk surface to position the head at different tracklocations. Current is passed to a voice coil motor (VCM) to position theactuator with respect to the disk surface. The amount of torque appliedto the actuator is governed by the amount of current in the VCM. The VCMcomprises the coil that receives the current and two magnets. Duringoperations, the disk drive components, such as the VCM, can producevibrations and oscillations induced as a result of the resonance of thecomponents. Such vibrations may result in undesirable head variationsand tracking errors.

Two factors that affect the access time that lapses before the head canaccess the disk include move time and settle time. The move time is thetime required for the head to move between tracks. The settle time isthe amount of time required, after the actuator has moved the headassembly during a seek, for the heads to stabilize sufficiently for thedata to begin to be read or written. The characteristics of the diskdrive system and environment can produce oscillations that may increasethe settle time and thereby degrade disk performance. Further, error mayresult if the head overshoots or undershoots the desired track.

In current disk drive systems, to correct for tracking errors resultingfrom noise and vibrations from components such as the VCM, the diskdrive controller will read servo information indicating the actualcurrent position and compare that value read to the desired position.This difference is known as the Position Error Signal (PES). The drivecontroller will then calculate a current to apply to the VCM to correctany variation in the measured position versus the desired position.Thus, the position feedback controller calculates the desired current tobe applied to the VCM to generate torque to move the actuator arm. Thecurrent is supplied by an amplifier between the feedback controlleroutput and the VCM input.

In some cases, the seek trajectory is optimized for seek speed to movethe actuator arm quickly, but it is also desirable for the head tosettle quickly over the correct data track. A typical approach is thebang-bang approach in which, for instance, a positive current moves thehead to the new position and a negative current brakes the head at thenew position. Such a current will appear as two step function pulses ofopposite polarity (i.e., a single square wave). The detailed physicsinvolved, however, makes the use of the bang-bang approach a non-idealsolution. A number of small modifications have been used for bang-bangVCM current vector to improve its performance by moving the head to thenew track quickly while minimizing the settle time at the desired track.One example involves the Fourier seek method as described in U.S. Pat.No. 6,549,364.

During an HDD seek operation, the actuator moves the head to the targetposition as quickly as possible. To reduce the seek time, the amplitudeof the current is increased using a generally square or rectangularwaveform. This will generate RTV (Random Transient Vibrations) due tomechanical motion and acoustic noise from propagation of the vibration.It is desirable to design the seek control trajectory with a smootherwaveform to produce smaller RTV and/or smaller seek acoustic noise, butthe existing design method involves trial and error and it may not beoptimum for specific actuator/drive dynamics.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide a method and a system forgenerating optimal feedforward signal for the seek control to suppressthe RTV and the seek acoustic noise. The seek curve is optimized basedon the actuator/drive dynamics, and the seek time is minimized. Thetechnique can be used for seek control using two degree-of-freedomcontrol (i.e., feedback and feedforward), whereby the feedforward signalis used to move the actuator on a desired trajectory. The feedbacksignal is used to correct the variance of the position error. Anadaptive filter is employed. First, the methodology provides adaptivefilter training to minimize the vibration and/or acoustic noise. Thenthe trained adaptive filter is implemented in the feedforward controlsystem to generate an improved feedforward signal for controlling theactuator or plant of the apparatus.

An aspect of the present invention is directed to a method of providinga revised feedforward signal using an adaptive filter in a feedforwardcontrol system for controlling an actuator to move a head to seek atrack and settle on the track of a disk in a disk drive apparatus. Themethod comprises performing a seek operation of the head using aninitial feedforward signal; obtaining an error signal at settling afterperforming the seek operation; determining filter characteristics of theadaptive filter to minimize the error signal; and implementing theadaptive filter having the determined filter characteristics in thefeedforward control system to produce a revised feedforward signal forcontrolling the actuator for moving the head in the disk driveapparatus.

In some embodiments, the initial feedforward signal is a bang-bang typefeedforward signal. The error signal comprises a position error signalor an acoustic noise or both a position error signal and an acousticnoise. The adaptive filter is a finite impulse response (FIR) filter.The adaptive filter has a constant DC gain corresponding to a desiredtrack seek length. Determining the filter characteristics comprisessolving for filter coefficients of the adaptive filter based on theerror signal. Solving for the coefficients of the adaptive filtercomprises using a Least-Mean-Square method to minimize a filter outputof the adaptive filter. Determining the filter characteristics comprisessetting an order of the adaptive filter initially to a small number andthen increasing the order if necessary until a filtered error signalbecomes sufficiently small to meet a target settling trackmisregistration (TMR).

In specific embodiments, the method further comprises, prior toimplementing the adaptive filter in the feedforward control system,using the revised feedforward signal to iteratively and repeatedlyperform the following to generate subsequent revised feedforward signalsuntil a desired condition of improved seek and settle of the head ismet: performing a seek operation of the head using a previous revisedfeedforward signal; obtaining an error signal at settling afterperforming the seek operation using the previous revised feedforwardsignal; determining filter characteristics of the adaptive filter tominimize the error signal using the previous revised feedforward signal;and using the adaptive filter having the determined filtercharacteristics in the feedforward control system to produce a currentrevised feedforward signal. In addition, different adaptive filters maybe used for different ranges of seek lengths, and the method comprisesdetermining the filter characteristics of the different adaptive filtersand implementing the different adaptive filters for the different rangesof seek lengths. The desired condition may comprise a target settlingtrack misregistration (TMR).

In accordance with another aspect of the present invention, a system forcontrolling an actuator to move a head to seek a track and settle on thetrack of a disk in a disk drive apparatus comprises a feedforwardcontroller configured to provide a feedforward signal; an adaptivefilter configured to filter the feedforward signal to generate afiltered feedforward signal; and an actuator configured to receive thefiltered feedforward signal for moving the head in the disk driveapparatus. The adaptive filter is trained to minimize an error signal ofperforming a seek operation of the head using the filtered feedforwardsignal.

In some embodiments, the adaptive filter is trained by performing a seekoperation of the head using an initial feedforward signal; obtaining anerror signal at settling after performing the seek operation;determining filter characteristics of the adaptive filter to minimizethe error signal; and implementing the adaptive filter having thedetermined filter characteristics in the feedforward control system toproduce a revised feedforward signal.

Another aspect of the invention is directed to a system for generating afeedforward signal for controlling an actuator to move a head to seek atrack and settle on the track of a disk in a disk drive apparatus. Thesystem comprises an adaptive filter configured to filter a feedforwardsignal to generate a filtered feedforward signal to be applied to theactuator for moving the head in the disk drive apparatus; and acomputer-readable storage medium including a computer program. Theprogram includes code for obtaining an error signal at settling afterperformance of a seek operation of the head using an initial feedforwardsignal to move the head in the disk drive apparatus; and code fordetermining filter characteristics of the adaptive filter to minimizethe error signal.

In some embodiments, the code for determining the filter characteristicscomprises code for solving for filter coefficients of the adaptivefilter based on the error signal. The code for determining the filtercharacteristics comprises code for setting an order of the adaptivefilter initially to a small number and then increasing the order ifnecessary until a filtered error signal becomes sufficiently small tomeet a target settling track misregistration (TMR).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a disk drive architecture in which aspects of the presentinvention may be implemented.

FIG. 2 is a schematic diagram of a feedforward control system in whichaspects of the invention may be implemented.

FIG. 3 is a schematic diagram of another feedforward control system inwhich aspects of the invention may be implemented.

FIG. 4 is a flow diagram of generating an improved feedforward signalusing adaptive filtering according to an embodiment of the presentinvention.

FIG. 5 is a schematic diagram illustrating an adaptive filter trainingscheme according to an embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating the implementation of atrained adaptive filter in a feedforward control system according to anembodiment of the present invention.

FIG. 7 shows simulation results of the original feedforward signal andthe improved feedforward signal after implementing the trained adaptivefilter in the feedforward control system.

FIG. 8 shows simulation results of the transfer function of actuatordynamics and the transfer function of the trained adaptive filter in thefeedforward control system.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a disk drive system 2, including one or more rotating disks4 (only one is shown), an actuator assembly 6 to move a head assembly 8across the disk 4 surface. The disk drive system 2 further includes acurrent driver 10 that converts the digital signal of a calculation fromservo electronics 12 or processor 18 to actual current that is appliedto a voice coil motor (VCM) 14. The VCM 14 comprises a coil that sitsbetween two magnets. The current driver 10 applies current to the VCM 14to cause the coil to react and move through a magnetic field to move theactuator 6.

In certain implementations, the head 8 is a magnetoresistive (MR) headdevice. However, in alternative implementations, the head 8 may beconstructed of other materials known in the art. The servo electronics12 provides a closed loop feedback system to ensure that the headfollows the tracks accurately and to control smooth transitions when thehead “seeks” from one track location to another track. The servoelectronics 12 calculates the position error signal (PES) from thedesired position and from pre-recorded servo information either on adedicated servo disk or on servo sectors interspersed among the datasectors on the disk. The servo electronics 12 uses the servo informationto determine the PES, which is the signal proportional to the differencebetween the ideal center line tracking and the actual positions of thehead assembly 8. The servo electronics 12 may then calculate acorrective position signal based on the PES. The actuator 6 pivotsaround a shaft 16 in response to the torque produced by the VCM 14.

A processor 18 manages read/write operations and controls other diskoperations. The processor 18 utilizes a volatile memory 20, such as arandom access memory (RAM) or registers as a working memory in whichinstructions and data are temporarily loaded for program execution. Anon-volatile storage 22, such as a read-only memory (ROM), programmableROM (PROM), erasable programmable ROM (EPROM), flash memory, etc.,stores program instructions and constants, referred to as code 26,loaded and executed by the processor 18 to perform the disk driveoperations. Alternatively, the code 26 described herein as performed byprocessor 18 along with the volatile memory 20 and non-volatile storage22 may be implemented as hardware, such as an Application SpecificIntegrated Circuit (ASIC).

FIG. 2 shows a feedforward control system 200 in which aspects of theinvention may be implemented. The reference signal r is processed by afeedforward controller 202 to produce a feedforward signal r′, which isthen combined with a feedback signal p to obtain (r′−p). The combinedsignal (r′−p) is processed by a controller 204 to generate a current,which is then applied to the actuator or plant 206 to produce an outputsignal that is used as the feedback signal p in the feedback loop. Thecombined signal (r′−p) represents an error signal such as the positionerror signal (PES) or the like.

FIG. 3 shows another feedforward control system 300 which may bereferred to as the model—following feedforward system. The referencesignal r is processed by a feedforward controller 302 to produce afeedforward signal r′. In one branch, the feedforward signal r′ isprocessed by the model (1/s²) 304, which represents a double integrationover time to generate a position signal from an acceleration signal. Theintegrated feedforward signal (1/s²)r′ is combined with a feedbacksignal p to obtain [(1/s²)r′−p]. The combined signal [(1/s²)r′−p] isprocessed by a controller 306 and then combined with the feedforwardsignal r′ to generate a current. The current is applied to the actuatoror plant 308 to produce an output signal that is used as the feedbacksignal p in the feedback loop. The combined signal [(1/s²)r′−p]represents an error signal such as the position error signal (PES) orthe like.

FIG. 4 is a flow diagram of generating an improved feedforward signalusing adaptive filtering according to an embodiment of the presentinvention. An adaptive filter is provided in a feedforward controlsystem. In step 402, the system performs the seek operation with anygiven feedforward signal. A signal for shorter seek time such as thebang-bang type is preferred. Step 404 involves collecting the errorsignal (e.g., the PES and/or the acoustic noise) at settling for somelength, i.e., after the feedforward control input signal becomes zero.In step 406, the adaptive filter equations are solved to obtain thefilter characteristics that will minimize the error signal and/or theacoustic noise, so as to reduce the settling time of the actuator. Inparticular, for example, the filter coefficients of the adaptive filterare calculated based on the error signal and/or noise signal using anadaptive technique such as the Least-Mean Square (LMS) method. See,e.g., Adaptive Signal Processing, B. Widrow and S. D. Stearns,Prentice-Hall, 1985. Steps 402–406 provide adaptive filter training. Instep 408, the trained adaptive filter is implemented in a feedforwardcontrol system to generate an improved feedforward signal.

FIG. 5 is a schematic diagram illustrating an adaptive filter trainingscheme (steps 402–406) according to an embodiment of the presentinvention. A feedforward signal (e.g., a bang-bang type signal) isapplied to an actuator or plant with closed loop feedback 502 to producean output signal representing an error signal with respect to areference signal (e.g., the PES). The error signal and/or the acousticnoise at settling for some length is/are collected. The adaptive filter504 is used to minimize the error signal and/or the acoustic noise. Theadaptive filter equations are solved to obtain the filtercharacteristics that will minimize the error signal and/or the acousticnoise, so as to reduce the settling time of the actuator and/or theacoustic noise.

The adaptive filter may be a finite impulse response (FIR) filter, aninfinite impulse response (IIR) filter, or the like. The FIR filter isgenerally preferred due to the finite impulse response characteristicsthat will produce a shorter settling time. The impulse response of theFIR filter whose order is N is assumed to be h(k). The order N of thefilter corresponds to the number of notches of the filter at whichminimum gain is sought to eliminate or reduce the effects of thevibration components. The error signal (e.g., PES) and the FIR filteroutput are designated as u(n) and y(n), respectively. The output of theadaptive filter (e.g., FIR filter) can be expressed as

${y(n)} = {\sum\limits_{k = 0}^{N}{{h(k)}{u\left( {n - k} \right)}}}$For a given seek length, a DC gain of the FIR filter is assumed to beequal to one.

${\sum\limits_{k = 0}^{N}{h(k)}} = 1$Then the filter output is

$\begin{matrix}{{y(n)} = {{\sum\limits_{k = 0}^{N - 1}{{h(k)}{u\left( {n - k} \right)}}} + {{h(N)}{u\left( {n - N} \right)}}}} \\{= {{\sum\limits_{k = 0}^{N - 1}{{h(k)}{u\left( {n - k} \right)}}} + {\left( {1 - {\sum\limits_{k = 0}^{N - 1}{h(k)}}} \right){u\left( {n - N} \right)}}}} \\{= {{\sum\limits_{k = 0}^{N - 1}\left\lbrack {{h(k)}\left( {{u\left( {n - k} \right)} - {u\left( {n - N} \right)}} \right)} \right\rbrack} + {u\left( {n - N} \right)}}}\end{matrix}$

The filter coefficients of the adaptive filter are calculated based onthe error signal and/or noise signal using an adaptive technique such asthe LMS method. The optimal filter h(k) minimizes the following

${y(n)} = {{\sum\limits_{k = 0}^{N - 1}\left\lbrack {{h(k)}\left( {{u\left( {n - k} \right)} - {u\left( {n - N} \right)}} \right)} \right\rbrack} + {{u\left( {n - N} \right)}.}}$Since many samples of the filter output is necessary to get accurateh(k), the following cost function is introduced and is minimized.

$J = {\sum\limits_{n = 0}^{M}{y(n)}^{2}}$The rest of the process is the same as the conventional LMS(Least-Mean-Square) method.

$\frac{\partial J}{\partial{h(i)}} = {{\sum\limits_{n = 0}^{M}\left\lbrack {2{y(n)}\frac{\partial{y(n)}}{\partial{h(i)}}} \right\rbrack} = {\sum\limits_{n = 0}^{M}\left\lbrack {2\left\{ {{\sum\limits_{k = 0}^{N - 1}\left\lbrack {{h(k)}\left( {{u\left( {n - k} \right)} - {u\left( {n - N} \right)}} \right)} \right\rbrack} + {u\left( {n - N} \right)}} \right\}\left\{ {{u\left( {n - i} \right)} - {u\left( {n - N} \right)}} \right\}} \right\rbrack}}$

If the following parameters are introduced, the equations will besimplified.

V_(i, k)(n) = {u(n − k) − u(n − N)}{u(n − i) − u(n − N)}W_(i)(n) = u(n − N){u(n − i) − u(n − N)}$\frac{\partial J}{\partial{h(i)}} = {{{\sum\limits_{n = 0}^{M}\left\lbrack {2\left\{ {\sum\limits_{k = 0}^{N - 1}\left\lbrack {{h(k)}{V_{i,k}(n)}} \right\rbrack} \right\}} \right\rbrack} + {\sum\limits_{n = 0}^{M}\left\lbrack {2{W_{i}(n)}} \right\rbrack}} = {{\sum\limits_{k = 0}^{N - 1}\left\lbrack {2{h(k)}\left\{ {\sum\limits_{n = 0}^{M}{V_{i,k}(n)}} \right\}} \right\rbrack} + {\sum\limits_{n = 0}^{M}\left\lbrack {2{W_{i}(n)}} \right\rbrack}}}$Since the optimal filter is at

${\frac{¶\; J}{¶\;{h(i)}} = {{0\mspace{14mu}{for}\mspace{14mu} 0} < i < {N - 1}}},$the matrix form is

$\begin{bmatrix}{- {\sum\limits_{n = 0}^{M}{W_{0}(n)}}} \\\vdots \\{- {\sum\limits_{n = 0}^{M}{W_{i}(n)}}} \\\vdots\end{bmatrix} = {{\begin{bmatrix}{\sum\limits_{n = 0}^{M}{V_{0,0}(n)}} & \; & \cdots & {\sum\limits_{n = 0}^{M}{V_{0,{N - 1}}(n)}} \\\vdots & \; & \cdots & \vdots \\{\sum\limits_{n = 0}^{M}{V_{i,0}(n)}} & \; & \cdots & {\sum\limits_{n = 0}^{M}{V_{i,{N - 1}}(n)}} \\\vdots & \; & \cdots & \vdots\end{bmatrix}\begin{bmatrix}{h(0)} \\\vdots \\{h\left( {N - 1} \right)}\end{bmatrix}}.}$Then the optimal filter impulse response is obtained as follows,

$\begin{bmatrix}{h(0)} \\\vdots \\{h\left( {N - 1} \right)}\end{bmatrix} = {\begin{bmatrix}{\sum\limits_{n = 0}^{M}{V_{0,0}(n)}} & \mspace{11mu} & \cdots & {\sum\limits_{n = 0}^{M}{V_{0,{N - 1}}(n)}} \\\vdots & \; & \cdots & \vdots \\{{\sum\limits_{n = 0}^{M}{V_{i,0}(n)}}\;} & \; & \cdots & {\sum\limits_{n = 0}^{M}{V_{i,{N - 1}}(n)}} \\\vdots & \; & \cdots & \vdots\end{bmatrix}^{- 1}\begin{bmatrix}{- {\sum\limits_{n = 0}^{M}{W_{0}(n)}}} \\\vdots \\{- {\sum\limits_{n = 0}^{M}{W_{i}(n)}}} \\\vdots\end{bmatrix}}$ ${h(N)} = {1 - {\sum\limits_{k = 0}^{N - 1}{{h(k)}.}}}$The coefficients of the FIR filter corresponds to these h(k) values.

The adaptive filter 504 has a constant DC gain corresponding to thedesired track seek length. During the training of the adaptive filter,the initial order of the filter can be set to a small number and thenincreased until the filtered error signal and/or acoustic noisebecomes/become sufficiently small to meet the target settling TMR (TrackMisregistration). More specifically, for example, the initial seekoperation is performed with a generic bang-bang seek trajectory or theparticular HDD's default seek trajectory. Steps 402–408 are performed toobtain the first ideal trajectory. Referring again to FIG. 4, step 410determines whether the desired condition(s) is or are met. If so, thetraining ends (step 411). If not, the system performs a seek operationwith an updated or revised feedforward signal using the updated adaptivefilter (step 412). Steps 412 and 404–408 are repeated in an iterativeprocess until the desired conditions are met (e.g., target settlingTMR).

Furthermore, different adaptive filters may be used for different rangesof seek lengths. For instance, optimum filter characteristics aredetermined for seek from the ID (inner diameter) to the OD (outerdiameter) of the magnetic disk, for seek from the ID to the MD (middlediameter), from the MD to the OD, and the like. This is desirable incases where the characteristics of the RTV changes depending on thelocation of the magnetic disk.

In FIG. 6, the trained adaptive filter 602 is implemented in afeedforward control system which may be any suitable system such asthose shown in FIG. 2 and FIG. 3. Since the transfer function from thefeedforward signal to the PES in FIG. 6 is the same as that from thefeedforward signal to the filtered PES in FIG. 5, the trained adaptivefilter also minimizes the PES in FIG. 6 when the filtered PES in FIG. 5is minimized. The trained adaptive filter 602 optimizes the feedforwardsignal to produce an improved feedforward signal which is then used todrive the actuator 604 to produce an output with a reduced error signaland/or acoustic noise so as to reduce the settling time of the actuator604.

FIG. 7 shows simulation results of the original feedforward signal andthe improved feedforward signal after implementing the trained adaptivefilter in the feedforward control system. The original signal 702 is thebang-bang type signal which produces a bang-bang type vibration 712 atsettling. After implementation of the trained adaptive filter in thefeedforward control system, the improved feedforward signal 704 producesa vibration 714 that has a much shorter settling time.

FIG. 8 shows simulation results of the transfer function of actuatordynamics and the transfer function of the trained adaptive filter in thefeedforward control system. The figure shows the magnitude 802 and phase812 of the transfer function of the actuator or plant dynamics, and themagnitude 804 and phase 814 of the transfer function of the trainedadaptive filter.

The above method may be implemented in software or firmware, and bestored in a computer-readable storage medium such as the non-volatilestorage 22 for execution by a computer processor such as the processor18.

It is to be understood that the above description is intended to beillustrative and not restrictive. Many embodiments will be apparent tothose of skill in the art upon reviewing the above description. Thescope of the invention should, therefore, be determined not withreference to the above description, but instead should be determinedwith reference to the appended claims along with their full scope ofequivalents.

1. A method of providing a feedforward signal using an adaptive filterin a feedforward control system for controlling an actuator to move ahead to seek a target track and settle on the target track of a disk ina disk drive apparatus, the method comprising: performing a first seekoperation to move the head to a first target track using an initialfeedforward signal; obtaining an error signal at settling after theinitial feedforward signal becomes zero; determining filtercharacteristics of the adaptive filter to minimize the error signal; andimplementing the adaptive filter having the determined filtercharacteristics in the feedforward control system to produce afeedforward signal for controlling the actuator for moving the head inthe disk drive apparatus during a second seek operation to move the headto a second target track.
 2. The method of claim 1 wherein the initialfeedforward signal is a bang-bang type feedforward signal.
 3. The methodof claim 1 wherein the error signal comprises a position error signal oran acoustic noise or both a position error signal and an acoustic noise.4. The method of claim 1 wherein the adaptive filter is a finite impulseresponse (FIR) filter.
 5. The method of claim 1 wherein the adaptivefilter has a constant DC gain corresponding to a desired track seeklength.
 6. The method of claim 1 wherein determining the filtercharacteristics comprises solving for filter coefficients of theadaptive filter based on the error signal.
 7. The method of claim 6wherein solving for the filter coefficients of the adaptive filtercomprises using a Least-Mean-Square method to minimize a filter outputof the adaptive filter.
 8. The method of claim 1 wherein determining thefilter characteristics comprises setting an order of the adaptive filterinitially to a small number and then increasing the order if necessaryuntil a filtered error signal becomes sufficiently small to meet atarget settling track misregistration (TMR).
 9. The method of claim 1further comprising, prior to implementing the adaptive filter in thefeedforward control system, using a revised feedforward signal toiteratively and repeatedly perform the following to generate subsequentrevised feedforward signals until a desired condition of improved seekand settle of the head is met: performing another seek operation of thehead using a revised feedforward signal produced from an adaptive filterhaving previously determined filter characteristics; obtaining an errorsignal at settling after performing the seek operation using the revisedfeedforward signal; and determining filter characteristics of theadaptive filter to minimize the error signal.
 10. The method of claim 9wherein the desired condition comprises a target settling trackmisregistration (TMR).
 11. The method of claim 1 wherein differentadaptive filters are used for different ranges of seek lengths, andwherein the method comprises determining the filter characteristics ofthe different adaptive filters and implementing the different adaptivefilters for the different ranges of seek lengths.
 12. The method ofclaim 1, where the first seek operation has a first seek length, andwherein the second seek operation has a second seek length substantiallyequal to the first seek length.
 13. The method of claim 1, furthercomprising: determining filter characteristics of different adaptivefilters for different seek lengths; and implementing an appropriateadaptive filter for a seek operation having a specified seek length,wherein the appropriate adaptive filter has filter characteristicsdetermined for that seek length.
 14. A system for controlling anactuator to move a head to seek a target track and settle on the targettrack of a disk in a disk drive apparatus, the system comprising: afeedforward controller configured to provide a feedforward signal; anadaptive filter configured to filter the feedforward signal to generatea filtered feedforward signal; and an actuator configured to receive thefiltered feedforward signal for moving the head in the disk driveapparatus to a second target track; wherein the adaptive filter istrained to minimize an error signal obtained at settling after aninitial feedforward signal becomes zero for a seek operation moving thehead to a first target track.
 15. The system of claim 14 wherein thefeedforward controller configured to provide a bang-bang typefeedforward signal.
 16. The system of claim 14 wherein the error signalcomprises a position error signal or an acoustic noise or both aposition error signal and an acoustic noise.
 17. The system of claim 14wherein the adaptive filter is a finite impulse response (FIR) filter.18. The system of claim 14 wherein the adaptive filter has a constant DCgain corresponding to a desired track seek length.
 19. The system ofclaim 14 wherein the adaptive filter is trained by: performing a firstseek operation to move the head to the first target track using aninitial feedforward signal; obtaining an error signal at settling afterthe initial feedforward signal becomes zero; and determining filtercharacteristics of the adaptive filter to minimize the error signal. 20.The system of claim 19 wherein determining the filter characteristicscomprises solving for filter coefficients of the adaptive filter basedon the error signal.
 21. The system of claim 20 wherein solving for thefilter coefficients of the adaptive filter comprises using aLeast-Mean-Square method to minimize a filter output of the adaptivefilter.
 22. The system of claim 19 wherein determining the filtercharacteristics comprises setting an order of the adaptive filterinitially to a small number and then increasing the order if necessaryuntil a filtered error signal becomes sufficiently small to meet atarget settling track misregistration (TMR).
 23. The system of claim 19wherein, prior to implementing the adaptive filter in the feedforwardcontrol system, using a revised feedforward signal to iteratively andrepeatedly perform the following to generate subsequent revisedfeedforward signals until a desired condition of improved seek andsettle of the head is met: performing another seek operation of the headusing a revised feedforward signal produced from an adaptive filterhaving previously determined filter characteristics; obtaining an errorsignal at settling after performing the seek operation using the revisedfeedforward signal; and determining filter characteristics of theadaptive filter to minimize the error signal.
 24. The system of claim 23wherein the desired condition comprises a target settling trackmisregistration (TMR).
 25. The system of claim 19 wherein differentadaptive filters are used for different ranges of seek lengths, andwherein the filter characteristics of the different adaptive filters aredetermined and implemented for the different ranges of seek lengths. 26.A system for generating a feedforward signal for controlling an actuatorto move a head to seek a track and settle on the track of a disk in adisk drive apparatus, the system comprising: an adaptive filterconfigured to filter a feedforward signal to generate a filteredfeedforward signal to be applied to the actuator for moving the head inthe disk drive apparatus; and a computer-readable storage mediumincluding a computer program which includes code for obtaining an errorsignal at settling after performance of a seek operation of the headusing an initial feedforward signal to move the head in the disk driveapparatus; and code for determining filter characteristics of theadaptive filter to minimize the error signal. wherein the code fordetermining the filter characteristics comprises code for setting anorder of the adaptive filter initially to a small number and thenincreasing the order if necessary until a filtered error signal becomessufficiently small to meet a target settling track misregistration(TMR).
 27. The system of claim 26 wherein the adaptive filter is afinite impulse response (FIR) filter.
 28. The system of claim 26 whereinthe code for determining the filter characteristics comprises code forsolving for filter coefficients of the adaptive filter based on theerror signal.
 29. The system of claim 28 wherein solving for the filtercoefficients of the adaptive filter comprises using a Least-Mean-Squaremethod to minimize a filter output of the adaptive filter.